1. Field of the Invention
The invention falls within the field of fluid flow inducers such as pumps and compressors and more specifically to those types of systems comprising syphons aspirators and ejectors.
The invention is a novel type of exhaust jet ejector which is particularly useful where efficient pumping operations must be performed under conditions of rapidly reversing flow such as that occurring at the side-port of an internal combustion engine cylinder during the alternate exhaust and induction cycles.
2. Description of Prior Art
The jet-ejector and its potential use was first concieved in the early part of this century in Europe by LeBlanc and in England by Parsons who are credited with the initial development.
In keeping with the general understanding, a jet-ejector, as described herein, is considered in the broadest sense as comprising a nozzle whose flow is directed into a diffuser. In this regard a nozzle is defined as any channel designed to increase fluid velocity and reduce stream pressure and conversly a diffuser is defined as any channel designed to reduce fluid velocity and increase stream pressure. Jet-ejectors operate on the principle of momentum exchange and should not be confused with the operation of venturis which depend principally on differential pressures for flow inducement in accordance with Bernoullis' principle.
During the engine exhaust cycle, at the end of the power stroke, the transfer of momentum from the exhaust stream to the air stream within the ejector is initially accomplished under compressible flow conditions with a net temperature decrease. Therefore the pumping action and inducement of air flow toward the diffuser is rather vigorous.
During the induction or intake stroke flow within the ejector air chamber is reversed toward the side-port nozzle. In this instance the flow is accomplished under low pressure ideal conditions and therefore the energy of the flow inducement in this direction is very low. For this reason, any turning losses incurred in the air stream entering the air chamber leading to the nozzle result in reduced velocity and increased dynamic flow losses which severely limit the quantity of air inducted into the engine and therefore decrease the volumetric efficiency.
Originally jet ejectors were designed as steady-state unidirectional flow systems and therefore the arrangement of relative flow paths within the ejector leading to the air chamber was not considered an important factor in the efficiency of the system. However, ejectors used in this particular application operate as pulse systems with rapidly reversing bidirectional flow paths. Therefore stream reversal must be accomplished within an extremely short period of time if the induction is to be effected in an efficient manner.
I have discovered that the bidirectional pulse type of jet-ejector can be made most efficient when the air supply to the air-chamber is directed in such a manner that its flow is directed toward the side-port nozzle. In this way, turning losses within the air-chamber are held to a minimum and stream reversal of the bidirectional flow is accomplished within the shortest period of time. In previous designs of this type of equipment, the direction of air flow to the air-chamber has been aligned in a parallel path with the exhaust flow from the side-port such that stream reversal during the induction phase was accomplished under conditions requiring 180.degree. reversal or turning losses. In the system listed in the cross references the reversal is executed at 90.degree. or slightly less when measured at the point of impingement between the nozzle and the diffuser. In the present invention air enters the air-chamber in a direction nearly opposite and nearly parallel to the exhaust flow from the side-port nozzle. Although the air stream is flowing in a nearly opposite direction its momentum is easily overcome by the vigous critical flow of the exhaust stream and is therefore turned toward the diffuser. However, during the induction cycle the air stream is directed toward the nozzle and therefore dynamic turning losses at the less vigorous ideal pressure conditions are held to a minimum.
The advantages of employing a bidirectional pulse jet ejector at the engine cylinder side-port is in the reduction of bottom-cycle pumping losses and in the reduction of thermal loads on the upper cylinder components. Efficiency losses occurring as a result of bottom-cycle pumping effort consist primarily of exhaust blowdown, exhaust stroke, and general flow losses during the induction stroke. The early evacuation of spent combustion gases through the side-port reduce the system pressure and exhaust mass decreasing the thermal load on the cylinder walls and on the exhaust poppet valve operating in the exhaust port of the upper cylinder head.